1. Field of the Invention
The present invention relates to a solenoid pump having a movable member, which is displaced by excitation of a solenoid section, wherein opened and closed states of a fluid passage are switched by displacement of the movable member.
2. Description of the Related Art
Heretofore, in the fields of chemistry and medicine, with the aim of analyzing the components included in liquids, or for mixing multiple liquids at predetermined proportional amounts or the like, liquid supply apparatus have been used, which are capable of supplying liquids in fine amounts. Such apparatus are equipped with a solenoid pump that causes fine amounts of liquid to be drawn in and delivered out, and are constituted so as to control the supply of such liquids at a desired amount.
As one such solenoid pump, there can be cited the fluid pump (fluid metering pump) disclosed in U.S. Pat. No. 5,284,425. In the disclosed fluid pump, by sliding movement of a movable member (plunger) due to excitation of a solenoid assembly, the movable member releases and opens an opening of an inlet side passage (inlet flow passage), which is normally blocked by the movable member, thereby placing the inlet side passage in communication with a pump chamber. More specifically, in the fluid pump of U.S. Pat. No. 5,284,425, accompanying a releasing action of the movable member, a desired amount of fluid (liquid) is drawn into the pump chamber from an upstream side fluid passage, and accompanying a blocking action of the movable member, the predetermined amount of fluid is caused to flow out from the pump chamber.
However, with the fluid pump of U.S. Pat. No. 5,284,425, the problems enumerated below are known to occur as a result of the movable member opening and closing the state of communication between the inlet side passage and the pump chamber.
First, from closing (blocking) of the inlet side passage through which fluid is drawn in by the movable member, because at this time the pump chamber remains in an open state of communication with the outlet side passage, it is easy for fluid that remains stored in the pump chamber and/or the outlet side passage to become contaminated. In particular, in the case that the fluid is a liquid, moisture tends to be removed from the interior of the pump chamber and via the outlet side passage, which leads to a concern that the liquid may become solidified. Also, in this case, disadvantages occur in that the amount of liquid that is drawn into the pump chamber tends to change, or undue time and labor must be expended when the interior of the pump chamber is cleaned, for example, when maintenance is performed thereon.
Secondly, because the discharged fluid is retained in a space made up of a comparatively large volume formed by the pump chamber and the outlet side passage, at a time when the movable member blocks the inlet side passage, a large amount of fluid is pushed out, which tends to cause large variations in the timing up to completion of outward flowing of the fluid (also referred to as liquid cut off, in the case that the fluid is a liquid). As a result, the amount of fluid that flows out from the outlet side passage is unstable.
Thirdly, in a state where the movable member blocks the inlet side passage, a membrane portion of the diaphragm that directly blocks the inlet side passage experiences changes and becomes warped over time, such that the volume of the pump chamber also undergoes changes. As a consequence, the fluid that flows into the pump chamber may be pushed out unexpectedly into the outlet side passage, causing leakage of the fluid to occur.